In radio communication it has been found advantageous to provide, below the upper rotary antenna array at the top of an antenna mast, a lower rotary antenna array rotatably mounted intermediate the top and bottom of the mast, and arranged to be rotated in synchronism with the upper antenna array, in order to create resonance with the upper antenna array. Mounting such a rotary lower resonance antenna array upon the mid-portion of a mast has hitherto also presented much difficulty, because of the difficulty of mounting a rotary bearing on the single upright involved therein. On the other hand, rotating the entire tower is even more difficult, for self-evident reasons. To mount such an antenna upon a tower composed of laterally spaced upright legs interconnected by struts, however, has hitherto prevented the mounting of such a lower antenna array because of the interference of the legs with the rotation of the lower antenna. The present invention is equally adaptable to mounting such an antenna upon a single upright, such as a mast, chimney or utility pole.